Aircraft, automobile and other transportation industries are continually seeking methods and materials to reduce weight of body structures in manufacturing. One method of weight reduction is accomplished by replacing heavier metal body panels and structures with lightweight metal or fiber reinforced polymer composite (FRP) panels in construction of body structures. These industries are aggressively perusing the use of FRP composite materials to reduce weight and improve fuel efficiency in aircraft and automobiles. A major issue in using composite and lightweight metal materials for the main body structure is the installation of fasteners and joining of parts onto the body structure during assembly of the aircraft or vehicle. Current methods of attaching fasteners and parts during assembly include using adhesives, mechanical fasteners or welding processes.
Thermoset adhesives, such as epoxy adhesives are commonly used to attach parts to metal or composite structures. These adhesives have short pot life (i.e., working time or usable life) and shelf life, and require long time periods to chemically react to set and cure. The manufacturing industry commonly uses thermoset adhesives with convection heat, hot plate and/or infrared radiation processing to join parts during assembly. One method of joining polymeric parts is by using polymeric adhesives. In this method, a thermoset adhesive is placed between the polymeric parts A and B to be joined. A hot air source is directed at the polymeric parts to heat the parts. The source heats the polymeric parts and polymeric adhesive and the thermoset adhesive is thermally cured by conduction heating.
Heating done by conduction has the limitations of being slow to heat the part and slow to cool off after processing and the heating process cannot be precisely controlled. Aerospace grade epoxy adhesive may take 3 to 7 days at ambient room temperature and 10 to 14 hours in a controlled autoclave system to fully cure. Attaching parts to a composite structure using thermoset adhesives is a time consuming and slow process. Detaching a conventional thermoset adhesive bonded part from the composite or metal structure is an intensive, time consuming task, and risks damaging the surface of the base structure.
Mechanical fasteners such as bolts or screws are attached by first drilling holes into the panel or body structure. Holes drilled into the body may produce stress points and material fatigue, a well-known issue in the industry. This is especially undesirable in composite panel structures where stress may cause composite panel delamination and structural failure over time. Using radiation or convection heat welding to attach parts to a composite substrate raises another issue. Conventional fiber-reinforced composite degrades when exposed to convection heat welding or radiation welding. For example, a fiber reinforced epoxy composite part surface may burn, decompose and/or delaminate when exposed to heat temperatures above 200° C. during the welding process.
Therefore, it is desirable to be able to bond parts onto reinforced polymeric composite and other lightweight substrate surfaces without using mechanical fasteners, welding processes or time-consuming thermoset adhesives in the manufacturing process. It is also desirable to be able to easily remove the parts from the composite structure in a repair process.